Cyanidation and flotation of ores



Jan. 5, 1937. v JJ. M. MORRIS 2,067,014

CYANIDATION AND FLOTATION OF CRES Filed Aug. s, 1935 2 sheets-sheet 1 0,1746 a z/f/P ro WASI-- ATTORNEY.

Jan. 5, 1937. L M MQRRB 2,067,014

CYANIDATION AND FLoTATIN oF oREs ATTORNEY.

" atented dan. 5, 1937 v attimi l 'Aramon or og .lehtlld Morris,

met "TV" P. l., a co i ration et ll Uli. invention relates to improvement in the cdation .im dotation of ores, especially gold Some gold ores contain both suldes and oximinerals and are far from homogeneous in structure, that is to say, they contain both hard and soft minerals, some of the latter frequently being relatively soluble in water and ute alkaline solutions. These ores present a lt serious problem when it is attempted to extract the ues by cyanidation. The soit terial tends to fo slimes `when sumcient grin is provided to reduce the harder minerals to thev es; i.. degree oi" neness. The slimes, particuw'larly if they contain soluble salts or are oi a coHoidal nature, cause serious tro .www cyanide plant; which not only reduces the capacity of the cyanide plant, but a concentration of values in the froth takes place through evaporation and through `the dotation action on certain u 1 l des'in the ore. Colloidal slimes alsotend to dmculate with .r i

into gelatinous docks when in contact .-1 solutions which are always present 'V in cyanidation and as this flocculation takes place in the presence of valuable solution, losses result because the enti-aimed solution cannot be removed trom these docksI by ordinary ltration. This rts in a loss both of values and of cyanide from the l #-fi also tends to slow thicke, clog nlter cloths d increase maintenance. Another serious loss rts when the ores contain soluble salts which act as cyanicides and conume lime. t 1:, w of these soluble salts which act as cyanicides also tend to form gelatinous compounds which increase the frothing.

The present invention is based on a separation, either partial mor complete, of the soft slimelo material from the harder ore and the healnnent of this separated portion by flotation preferably with return of flotation concentrat. to the cyanide plant in which the harder portion ofthe ore is treated. The separation of the slimes may bei at various points between the M ori ore and the actualvtreatment in the cyanide plant. Thus, with many ores such as, for

t; t n gold ore found extensively in the Philippines, a very large proportion of the slimes are 4 present in such a form-that they are separated by. c and washing. With some of these ores,' therefore, it is desirable to eect slime separation at this point. Where, however, there is a large amount of soft material which does not form a separable slimeby crushing and washing,l it is frequently advantageous to edect the sepaa solution. 'The occulant maim. 'l5-2l ration also at a further point by a p grinding of the ore in water after crushing and separation of the slime.

Normally, the slimes removed after crushing and ng followed by screening, and also the slimes produced by primary grinding in water where this is used, require classication. In the case of the slimes obtained from crushing and washing, this classification is frequently carried on in more than one stage. Normally, a single stage of classification sumces in separating the slimes produced by pry grinding in water. The invention is in no sense concerned with any particular arrangement of classification and the ner oil stages and nature of `the equipment will, oi course, vary with the vteristics of the shines produced which, in turn, are determined by the character of the ore. It is an advantage of the present invention that no special typesiof clessiiders are necessary. In general, the usual types of classiers such as rake classiilers and bowl classiers and the like may be used. ln fact, thepres'ent invention requires no special type of equipment not ordinarily used in ore dressing.4

ere slimes from crushing and :l classified in more one stage, the jected in these stages may be returned to the coarser material at various points along its travel to the cyanide plant. The particular arrangement of dow sheet will depend on the ore and on the equipment aable in the plant, and other factors.

The slimes, after suitable separation and, if

' necessary, after adjustment of the solid content, are subjected to flotation which can be edected in any standard type of dotation me.

The present invention greatly -increases the capacity of a given cyanide plant since a considerable proportion oi the ore never ses through the cyanide-plant and frothing dimculties are eliminated which permit a greater mei l :w efficiency for a given cyanide plant. Also, since the components of the ore, which cause cyanide, gold and lime losses in the cyanide plant, are partially or Wholly removed, the

chemical emciency of the cyanide plant is materially increased. lt is a further advantage of the present invention that the greatly increased mechanical and chemical emcency ofthe cyanide plant is obtained without a corresponding loss, since the slimes which cause diflculty in the cyanide plant are normally readily amenable to flotation, so that they are treated in the flotation circuit under conditions which make for` real 55 tration of this factor is found in the case of many of the soluble salts which cause serious lime or cyanide losses in a cyanide plant but which are actually beneficial in flotation. Because both the cyanide plant and the flotation plant are operated under, very efiicient conditions, the total size of a plant for treating a given amount of ore ismaterially reduced and the cost is likewise reduced. Representative plants embodying the present invention on Philippine gold ores are approximately one-third cheaper to build than an all cyanide plant of equal capacity, and milling and maintenance costs are markedly reduced.

The present invention should not be confused with processes which have been proposed in which all of the ore is treated by flotation and the flotation concentrates or tails are then cyanided. Such a process with the slime-forming ores for which the present invention is particularly suitable, does not give satisfactory results because the reagent cost for otation of the-total feed is excessive and tailing losses are unduly high. Apparently, the gold in the slimes is in a form which is much more amenable to otation at moderate reagent costs.

In the present invention the two types of minerals in the precious metal ore, i. e. hard and soft, are each treated by a process which is best adapted for metallurgical elciency on each type of mineral. Another advantage of the present invention in most of theores tending to slime formation, lies in the fact that the slimes carry a smaller concentration of .gold ory other precious metal. Therefore, the removal of the slimes results in a concentration ofvalues in the remaining sands. It is these more concentrated portions which are treated in the cyanide plant with the more expensive and more efficient equipment. The lower grade material is treated by the otation process which is cheaper per ton and which, with this material, gives very satisfactory recoveries. This economic advantage can beutilized in various ways which will vary with the conditions of a particular mill. Thus, lower milling costs can be obtained with approximately the same or slightly higher recoveries, or the reduction in milling cost, which is brought about byv removing the slimes and treating them by flotation, can be partly or wholly used in a more thorough grind of the sands or a more extensive cyanidation, thus resulting in higher recovery for approximately the same milling costs. 'I'he best compromise will, of course, be chosen by the skilled plant engineer, taking into consideration the factors of a given mill. It is an advantage of the present invention that it is very exible and is therefore not only applicable to new mills but can be effectively utilized in improving or expanding cyanide mills which have already been constructed. The fieidbility of the invention also permits varying the procedure in a given mill with different market or ore conditions.

The present invention is `not limited to any particular notation reagents, the usual xanthates with pine oil or other frothers giving satisfactory results. Other collectors may, of course, be used such as dithiophosphates.

The invention will be described in'detail in connection ,with the drawings in which:

Fig. 1 is a iiow sheet of a process embodying the present invention; and

Fig. 2` is a modified flow sheet providing preliminary grinding of sands prior to final grinding in cyanide solution.

otation eillciency. A particularly striking illus- Fig. 1 is a ow sheet showing the notation of a typical ore mined at Benguet Consolidated Mining Company in the Philippines. The original ore carrying about $15.80 of gold per ton, is screened, crushed in a jaw crusher and again screened, the coarse ore being fed to a cone crusher, and the slimes and fine ore to a classier. The underflow of the classier joins the ground coarse ore from the cone crusher and is then given a primary grinding in a ball mill. The s es or overiiow are transferred to a' bowl classifier from which the dragover joins the discharge from the primary ball mills and is subjected to secondary grinding in cyanide solution. 'I'he bowl classier overflow which is 90% below 200 mesh'and which contains about $9.10 work of gold per ton, is then thickened to 13% solids and floated in' a string of standard Fagergren flotation machines in a circuit having a pH between 6.6 and 6.8 (obtained, if necessary. by adding sulfuric acid). .05 lbs. of secondary butyl xanthate is added with the sulfuric acid and the pulp, after conditioning, flows into otation cells where .2 lb. per to'n of pine oil is added as a frother. 'I'he tails, whichcontain approximately 93 cents of gold, are discharged to waste and the concentrates carrying about $129.00 of gold per ton are regroundin cyanide in the secondary grinding circuit before passing through the remainder of the cyanide plant which is of standarddesign and uses a solution containing approznmately 1.34 lbs. NaCN equivalent and L34 lbs. CaO per ton. A tail of slightly over a dollar is obtained. The capacity of the cyanide plant is increased about 50% and all frothing troubles are eliminated. f

The above description applies to a modication ofthe invention in which slimes are removed only after crushing `and washing and represents the first method of application of the present invention to Benguetore. With this particular ore, still further savings are being effected by giving thercrushed ore after slime separation and the sand from the rst classier a preliminary grind in .water followed by separation of sands and slime in an additional bowl classifier, the overflow going to the flotation circuit and the sands being ground and cyanided. This'modiied procedure which isillustrated in Fig. 2 not only still further decreases the amount of slimes and soluble salt present in the cyanide plant, but an enrichment or concentration ,of the gold values in the sands which are treated in the cyanidation plant is effected, due to the fact that the slimes formed in the primary grind in water have a lower gold content than the material fed into the primary grinding circuit.

'I'he use of the present invention as described above' at the mill of the Benguet Consolidated Mining Company at Baguio. P. I., resulted in increasing the mechanical capacity of the cyanide plant from 485 to 778 tons per day. Frothing is less at the higher capacity than formerly at the lower capacity. Losses through froth are entirely eliminated and the actual amount of froth at 778 tons is only one tenth of what it used to be'on 485 tons before the plant was remodeled to incorporate the present invention.

The life of iilter covers in the cyanide plant was approximately doubled; solution pump life quadrupled, and the milling costs reduced more than 25%. Lime consumption was decreased from approximately 15 lbs. per ton to about 6 lbs. per ton. A saving of one-tenth 1b. NaCN equivalent per ton of ore was also eected.

While the present invention is particularly effective with vslimey ores which cause serious frothing trouble in the cyanide plant, it may, of

course, be applied to ores which can be directly cyanided and the advantages of the present invention in increased cyanide plant capacity and better metallurgy are obtained, although, of course, they are not so marked as with ore which slimes badly.

The invention has been described in conjunction with ores where ilotation and concentration is amenable to cyanidation. This is the preferred embodiment of the invention but with some ores it may be desirable to adopt other methods of recovering the values from the flotation concentrate. This is particularly true where the softer type of minerals may contain metals other; than the precious metals which would render cyanidation of the iiotation concentrate uneconomical.

I claim:

1. A method of treating precious metal ores which contain both hard and soft types of minerals which comprises separating at least a portion of the softer type minerals from the ore, l.

treating this separated portion by a process including iiotation, and treating the portion of the ore containing the harder type minerals by cyanidation and recovering values from the flotation concentrate. Y Y

2. VA method of treating precious metal ores ,which contain bothhardand soft types of minerals, which comprises separating at least'a portion of the softer type minerals from the ore, treating this separated portion by a process including iiotation and treating the portion of the ore containing the harder type minerals together with the ilotation concentrates by cyanidation, and recovering values from the otation concenv trate.

, 3. A method of treating precious metal ores which contain minerals tending to form slimes, which comprises crushing and washing the ore, separating shines, classifying-the slimes, floating the classified slimes with a flotation reagent capable of iioating precious metals and subjecting which contain minerals tending to form slimes,'

which comprises crushing and washing the ore,

separating slimes, iioating the slimes with a iiota-V tion reagent capable of floating precious metals and subjecting the coarser portions of the crushed ore .and the flotation concentrates to cyanidation.

5. A method of treating precious metal ores which contain minerals tending to formslimes on crushing and grinding, which comprises crushing and washing the ore, separating the slimes from the coarse portions, subjecting the coarse ore to at least one stage of a preliminary grinding in water with concomitant production of slimes, separating the slimes thus produced, oating the slimes with a otation reagent capable of oating precious metals and subjecting the sands from the preliminary grinding as well as the otation concentrates to cyanidation.

6. A method of treating precious metal ores which contain minerals tending to form slimes on crushing and grinding, which comprises crushing and washing the ore, separating the slimes from the coarse portions, subjecting the coarse ore to at least one stage of a preliminary grinding in water with concomitant production of slimes, separating the slimes thusproduced, classifying the slimes, floating the classied slimes with a otation'reagent capable of otation of precious metals and subjecting the sands from the preliminary grinding and from slime classi- Aication as well as the flotation concentrates to cyanidation.

'1. A method according to claim 5 in which at least a portion of the sands from the slime classiiication are subjected to the preliminary grinding in' water. A

8. A method according to claim 6 in which at least a portion of the sands from the slime classication are subjected to the preliminary grinding in water. 1

JEPHTHAH M. MORRIS. 

